This project involves utilization of single neuron recording and operant conditioning techniques in behaving monkeys to study brain mechanisms underlying voluntary movement. Monkeys are trained to make precise movements of a handle whose rotation controls a visual display, and stimuli are delivered via the handle by means of an electronically controlled torque motor in order to determine how sensory feedback is processed. Red nucleus neurons (Rnns) failed to show changes in frequency preceding EMG changes of arm muscles discharging in advance of large, high velocity movements, with RNN discharge starting at movement onset or during movement and peaking near movement termination. In contrast to this terminal peaking of RNN discharge, the activity of the muscles usually peaked around movement onset, and early peaking was also seen for both precentral and postcentral pyramidal tract neurons. The observed RNN discharge patterns fit nicely with their putative role in regulation of reflex excitability with different phases of movement.